Our long-term goal is to contribute to the eradication of HIV infection by finding strategies to eliminate latency. HIV-1 infection escapes eradication by establishing a latent reservoir. Consequently, identification of cellular factors implicated in the establishment or maintenance of latency, which is the focus of this application, could reveal new therapeutic targets for suppression of HIV-1 infection. We have recently discovered a novel role of PARP-1 in silencing HIV-1 gene expression in human CD4+ T cells. Our data indicated that PARP-1 knockdown (KD) CD4+ T cells are up to 90-fold more permissive to HIV-1 replication than control cells. Furthermore, re-expression of PARP-1 in the KD cells substantially diminished their susceptibility to HIV-1. In addition, a small molecule that targets the zinc finge domains of PARP-1, but not inhibitors binding to the active site of this enzyme, also increased viral replication in CD4+ T cells by 60-folds. Importantly, HIV-1 DNA integration or the production phase of the HIV-1 life cycle were not affected by PARP-1 deficiency or pharmacological interference, indicating that PARP-1 affects HIV-1 replication at a post-integration step, more likely at the level of gene expression. Notably, the effect of PARP-1 required CD4/CXCR4-mediated viral entry; i.e. PARP-1 did not affect infection by VSV-G pseudotyped viruses. Based on these results, we envision that PARP-1 negatively regulates HIV Env-induced CD4/CXCR4 signaling, limiting in this manner the availability of specific transcription factors and consequently favoring the establishment of latency. Multiple findings support our central hypothesis: (1) HIV Env-induced CD4/co-receptor signaling increases expression of cellular factors (i.e. NF-ATs, AP-1, and NF-kB) that promote viral replication. (2) PARP-1 negatively regulates the transcription of multiple genes induced by T cell activation, in part through inhibition of NF-AT- or NF-kB-dependent transcription. (3) HIV-1 gene expression is largely influenced by the availability of specific cellular transcription factors and latency is favored in transcription factor-deprived cells. We are well positioned to carry out the proposed studies because of our extensive experience in the characterization of the molecular mechanisms of cellular cofactors in HIV replication, and in particular in PARP-1. Collaborations established with experts in HIV-1 latency and T cell signaling fields will complement and very efficiently synergize with our own expertise in these fields. At the conclusion of this research we expect to have defined the role of PARP-1 in HIV latency and better identified its mechanism of action. The work proposed is important because new therapeutic targets to eradicate HIV infection could be discovered.